Peristaltic pumps with reduced pulsations

ABSTRACT

Systems and methods are disclosed for reducing pulsations in peristaltic pumps. In some examples, a cassette comprises a cassette body and a flexible sheet joined to the cassette body, wherein a transition region of the flexible sheet comprises at least one ridge that has a maximum height at a position that is offset from a center line of a cassette body transition channel. In some examples, a cassette body transition channel comprises side walls that taper toward an active region of the fluid path and/or toward a bottom of the transition channel. An example method of operating a peristaltic pump comprises operating rollers at a higher speed during portions of a revolution that otherwise would result in a lower than average flow rate and at a lower speed during portions of the revolution that otherwise would result in a higher than average flow rate.

TECHNICAL FIELD

The present disclosure is directed to systems and methods relating toperistaltic pumps used, for example, during ophthalmic surgery.

BACKGROUND

In ophthalmic surgical procedures, fluids are often aspirated from theeye during the procedure. For example, in vitreoretinal surgery, adevice may be used to aspirate vitreous material from the eye. Asanother example, in cataract surgery, a device may be used to fragmentor emulsify a lens and to aspirate the broken or emulsified lens fromthe eye.

In addition, in some ophthalmic surgical procedures, it may be desirableto infuse fluid into the eye. For example, in vitreoretinal surgery,cataract surgery, or other procedures, a balanced salt solution (BSS) orother irrigation fluid may be introduced into the eye. The fluid may beremoved during the procedure as part of the aspirated fluid.

In such ophthalmic surgical procedures, a peristaltic pump may be usedfor aspiration and/or infusion of fluid. Peristaltic pumps are a type ofpositive displacement pump often used in medical devices because of thelimited contact between the pump and the fluid. In a typical design, thepumped fluid makes contact only with an easily removable component ofthe pump system. To achieve flow, the fluid is present in a flexibleconduit that is locally collapsed to the point of blocking flow. Thesealing point is moved along the conduit in the direction of the flow.To achieve an unlimited flow, this deformation of the conduit isrepeatedly produced at multiple locations along the conduit such as byusing a set of rollers mounted on a rotating hub with the flexibleconduit located adjacent to the rollers.

In some prior systems, a peristaltic pump includes an elastomeric sheetjoined to a rigid cassette body, wherein one or more fluid channels areformed in the space between the elastomeric sheet and the cassette body.Rollers mounted on a rotating hub press the elastomeric sheet to producethe pumping action.

Prior systems for fluid aspiration and/or infusion using a peristalticpump are disclosed in U.S. Pat. Nos. 6,261,283, 6,293,926, 6,572,349,6,632,214, 6,740,074, 6,902,542, 6,962,488, 7,393,189, 7,775,780,8,011,905, 8,545,198, 8,790,096, 9,482,216, and 9,931,447, thedisclosures of which are hereby incorporated by reference herein intheir entirety.

Typically, in a peristaltic pump, the flow is nonconstant with aperiodic flow. For example, a flow profile that repeats with the passageof each roller is typical. Prior attempts have been made to reducepulsations in peristaltic pumps in order to achieve a more stable flowrate. For example, U.S. Pat. No. 6,293,926 discloses an elastomericsheet having tapered channel transition regions, wherein the channeltransition regions of the elastomeric sheet have internal cross-sectionsthat taper from zero to the full cross-section of the channel. U.S. Pat.No. 7,775,780 discloses a cassette body wherein the bottom surfaces ofchannel transition regions in the cassette are tapered toward theelastomeric sheet to correspond to the shape of the tapered channeltransition regions of the elastomeric sheet, in order to providetransition channel regions between the cassette and sheet that have arelatively constant cross-section. U.S. Pat. No. 8,790,096 disclosesother designs intended to reduce pulsations, such as a peristaltic pumpwith two pump conduit segments in which the rollers acting on one pumpconduit segment are out of phase with the rollers acting on the otherpump conduit segment.

While these prior designs have had some success in reducing pulsationsin peristaltic pumps, there is a continuing need for improved designsfor reducing pulsations in peristaltic pumps.

SUMMARY

The present disclosure is directed to improved systems and methods forreducing pulsations in peristaltic pumps.

In some example embodiments, a cassette for a peristaltic pump of anophthalmic surgical system comprises a cassette body and a flexiblesheet joined to the cassette body, wherein a transition region of theflexible sheet comprises at least one ridge that has its maximum heightat a position that is offset from a center line of a transition channelof the cassette body. The transition region of the flexible sheet maycomprise an indentation at a position over the center line of thetransition channel of the cassette body. The sheet thickness at theridge may be greater than the sheet thickness at the indentation.

In some example embodiments, the transition region of the flexible sheetmay comprise a plurality of ridges that have their maximum heights atpositions that are offset from the center line of the transition channelof the cassette body. The transition region of the flexible sheet maycomprise two ridges, each of which has its maximum height at a positionthat is offset from the center line of the cassette body transitionchannel. One of the two ridges may be on one side of the indentation,and the other of the two ridges may be on an opposite side of theindentation. The two ridges of the transition region of the flexiblesheet may merge into a single ridge in an active region of the flexiblesheet.

In some example embodiments, a cassette for a peristaltic pump of anophthalmic surgical system comprises a cassette body and a flexiblesheet joined to the cassette body, wherein a cassette body fluid pathtransition channel comprises a first end adjacent a port, a second endadjacent an active region, and side walls, and wherein a distancebetween the side walls tapers toward the second end. In some exampleembodiments, a distance between the side walls tapers toward a bottom ofthe cassette body fluid path transition channel.

In some example embodiments, a method of operating a peristaltic pumpcomprises operating a set of rollers at a speed higher than a nominalspeed during portions of a revolution of the set of rollers that wouldresult in a lower than average fluid flow rate if the set of rollerswere operated at the nominal speed, and operating the set of rollers ata speed lower than the nominal speed during portions of the revolutionof the set of rollers that would result in a higher than average fluidflow rate if the set of rollers were operated at the nominal speed. Theset of rollers may be operated in a plurality of compensation cycles,with each compensation cycle going to a speed higher than the nominalspeed then to a speed lower than nominal speed. The set of rollers maybe operated in a plurality of compensation cycles per revolution of theset of rollers. In some example embodiments, the number of compensationcycles per revolution of the set of rollers may be equal to the numberof rollers of the peristaltic pump multiplied by the number of pumpsegments of the peristaltic pump.

In some example embodiments, the set of rollers is operated inaccordance with a compensation profile that determines the speed of theset of rollers. The compensation profile may be a fixed profile or avarying profile. For example, the compensation profile may varydepending on the speed of the set of rollers. The compensation profilemay be determined during the operation of the peristaltic pump or priorto the operation of the peristaltic pump. The compensation profile maybe associated with indicia located on a removable portion of theperistaltic pump.

These and other examples will be understood by persons having ordinaryskill in the art based on this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate examples of the systems and methodsdisclosed herein and, together with the description, serve to explainthe principles of the present disclosure.

FIG. 1a illustrates a front view of an elastomeric sheet with two pumpconduit segments, as disclosed in U.S. Pat. No. 8,790,096.

FIG. 1b illustrates a back view of the elastomeric sheet of FIG. 1a , asdisclosed in U.S. Pat. No. 8,790,096.

FIG. 1c illustrates a front view of a cassette body with two pumpconduit segments, as disclosed in U.S. Pat. No. 8,790,096.

FIG. 1d illustrates a back view of the cassette body of FIG. 1c , asdisclosed in U.S. Pat. No. 8,790,096.

FIG. 2 illustrates a cross-section taken along the line 2-2 in FIG. 1c ,showing the cross-sectional view at that plane with the elastomericsheet of FIGS. 1a-b assembled on the cassette body of FIGS. 1c -d.

FIG. 3 illustrates a cross-sectional view of a part of a first exampleof a peristaltic pump in accordance with the disclosure.

FIG. 4 illustrates a top view of a part of a second example of aperistaltic pump in accordance with the disclosure.

FIG. 5 illustrates an enlargement of a cassette body fluid pathtransition channel of FIG. 4.

FIG. 6 shows a graph comparing a prior peristaltic pump system operatedat a constant speed with a peristaltic pump operated at varying speedsin accordance with the disclosure.

FIG. 7 shows a graph of a compensation profile for operating aperistaltic pump at varying speeds in accordance with the disclosure.

The accompanying drawings may be better understood by reference to thefollowing detailed description.

DETAILED DESCRIPTION

For the purposes of explaining the principles of the disclosure,reference is made to the drawings, and specific language is used todescribe the same. It will nevertheless be understood that no limitationof the scope of the disclosure is intended. Any alterations and furthermodifications to the described systems, devices, instruments, andmethods, and any further application of the principles of the presentdisclosure, are fully contemplated as would normally occur to oneskilled in the art to which the disclosure relates. In particular, thefeatures, components, and/or steps described with respect to one exampleof the disclosure may be combined with features, components, and/orsteps described with respect to other examples of the disclosure. Forsimplicity, in some instances the same reference numbers are usedthroughout the drawings to refer to the same or like parts.

FIGS. 1a-1d illustrate a flexible sheet 107 and rigid cassette body 105as shown in FIGS. 1a-1d of U.S. Pat. No. 8,790,096. The flexible sheet107 and cassette body 105 may constitute parts of a cassette for aperistaltic pump of an ophthalmic surgical system, for example parts ofa cassette as may be used with an ophthalmic surgical console. The term“cassette” as used herein refers to a component of a peristaltic pumpthat includes a fluid path for the pumping action; the cassette may ormay not be removable from the ophthalmic surgical console. Theophthalmic surgical console may be similar to ophthalmic surgicalconsoles as shown and described in U.S. Pat. No. 9,931,447. Theophthalmic surgical console may be similar to ophthalmic surgicalconsoles that have been known and used, such as the CONSTELLATION®Vision System available from Alcon Laboratories, Inc. (Fort Worth, Tex.)or the CENTURION® Vision System available from Alcon Laboratories, Inc.(Fort Worth, Tex.), or any other ophthalmic surgical console suitablefor use with the principles described herein.

The ophthalmic surgical console typically includes one or more systemsthat may be used in performing an ophthalmic surgical procedure. Forexample, the console typically includes a fluidics system that mayinclude an aspiration system for aspirating fluid from an eye and/or andinfusion system for infusing fluid into the eye. The fluidics system maybe similar to fluidics systems as shown and described in U.S. Pat. No.9,931,447, or similar to fluidics systems that have been known and used,such as in the CONSTELLATION® Vision System or in the CENTURION® VisionSystem, or similar to any other fluidics system suitable for use withthe principles described herein.

The sheet 107 and cassette body 105 as shown in FIGS. 1a-1d mayconstitute parts of a cassette that may be used with the fluidics systemof the ophthalmic surgical console. The cassette may be similar to acassette as shown and described in U.S. Pat. No. 9,931,447, or similarto cassettes that have been known and used, such with the CONSTELLATION®Vision System or the CENTURION® Vision System, or similar to any othercassette suitable for use with the principles described herein. Theconsole may have a set of rollers that are mounted for rotation on arotary hub. The hub and rollers and cassette (or a portion of thecassette) may together form a peristaltic pump (other components such asa peristaltic pump motor may be included as well).

The sheet 107 may be made of a flexible material such as silicone rubberor a thermoplastic elastomer. Other flexible materials may be used. Theterm “flexible” when used with respect to a sheet as described hereinmeans that the sheet has sufficient flexibility such that it can bedeformed for pumping action. The sheet 107 may be one piece or multiplepieces. The sheet may be made by molding or any other suitable method.

The cassette body 105 may be made of a rigid material, such as a rigidthermoplastic material, for example polycarbonate and/or polysulfone, toprovide rigidity and structure. The cassette body 105 may be one pieceor multiple pieces. The cassette body may be made by injection molding,machining, or any other suitable method. The cassette body 105 may havea pump interface portion which may be engaged by the elastomeric sheet107 in order to form the pump fluid path, with pump segments of thesheet to be engaged by the pump rollers. Portions of the aspiration flowpath and/or infusion flow path may extend as channels and/or tubesinside the cassette body 105.

The cassette body 105 may be provided with holes and/or notches foraligning the cassette with the console when the cassette is loaded intothe console. In some examples, the cassette may be a removable anddisposable or consumable item that can be used for a single patientprocedure. A new cassette may be used for a new procedure.

As described in U.S. Pat. No. 8,790,096, the sheet 107 is adapted to becoupled to the cassette body 105 to define two or more pump fluid pathsof the joined sheet 107 and cassette body 105, in the areas designatedas sheet pump segments 103 a, 103 b (collectively, pump segments 103).In some examples, the sheet 107 may be bonded or mechanically attachedto the cassette body 105 (e.g., through adhesive, heat fusion,mechanical crimping, rivets, etc.). In some examples, protrusions suchas protrusions labeled 151 a-n on an outer perimeter and/or interior ofthe sheet 107 may engage corresponding recesses such as recesses labeled153 a-n on cassette body 105 to connect the sheet 107 to the cassettebody 105 and help prevent rotation of the sheet 107 when acted upon byrollers.

As can be seen in FIGS. 1c and 1d , the cassette body 105 has a frontsurface 121 and a back surface 123. The front surface 121 has a pumpinterface portion 109 that includes cassette body fluid paths 125 a, 125b. Cassette body fluid path 125 a comprises an inlet port 112 a and anoutlet port 112 b, a cassette body fluid path active region 163, acassette body fluid path transition region 127 a between the inlet port112 a and the cassette body fluid path active region 163, and a cassettebody fluid path transition region 127 b between the outlet port 112 band the cassette body fluid path active region 163. Cassette body fluidpath 125 b comprises an inlet port 112 c and an outlet port 112 d, acassette body fluid path active region 165, a cassette body fluid pathtransition region 127 c between the inlet port 112 c and the cassettebody fluid path active region 165, and a cassette body fluid pathtransition region 127 d between the outlet port 112 d and the cassettebody fluid path active region 165. Each of the cassette body fluid pathtransition regions 127 a, 127 b, 127 c, 127 d comprises a cassette bodyfluid path transition channel 157 a, 157 b, 157 c, 157 d, respectively,that is recessed with respect to the adjacent cassette body fluid pathactive region 163 or 165.

As can be seen in FIGS. 1a and 1b , the flexible sheet 107 has a frontsurface 131 and a back surface 133. The flexible sheet 107 comprisessheet pump segments 103 a, 103 b. The back surface of each sheet pumpsegment 103 a, 103 b defines a sheet fluid path 135 a, 135 b,respectively. The front surface of each sheet pump segment 103 a, 103 bcomprises a roller engagement surface 137 a, 137 b, respectively. Thesheet pump segment 103 a comprises a sheet pump segment active region143 adapted to be positioned over the cassette body fluid path activeregion 163, a sheet pump segment transition region 147 a adapted to bepositioned over the cassette body fluid path transition region 127 a,and a sheet pump segment transition region 147 b adapted to bepositioned over the cassette body fluid path transition region 127 b.The sheet pump segment 103 b comprises a sheet pump segment activeregion 145 adapted to be positioned over the cassette body fluid pathactive region 165, a sheet pump segment transition region 147 c adaptedto be positioned over the cassette body fluid path transition region 127c, and a sheet pump segment transition region 147 d adapted to bepositioned over the cassette body fluid path transition region 127 d.

In the example of FIGS. 1a-d , protrusions 117 a, 117 b on the sheet 107(which may outline the respective sheet fluid paths 135 a, 135 b) mayfit into corresponding recesses 119 a, 119 b in the cassette body 105(which may outline the respective cassette body fluid paths 125 a, 125b). When the flexible sheet 107 is joined to the cassette body 105, thesheet fluid path 135 a is connected with the cassette body fluid path125 a to form a first pump fluid path, and the sheet fluid path 135 b isconnected with the cassette body fluid path 125 b to form a second pumpfluid path.

Protrusions 117 a, 117 b may be secured to the respective recesses 119a, 119 b to retain the sheet 107 to the cassette body 105. In someexamples, protrusions 151 a-n and/or protrusions 117 a, 117 b may besecured to respective recesses 153 a-n and/or recesses 119 a, 119 bthrough a mechanical/friction fit, adhesive, heat fusion, etc. In someexamples, protrusions 117 a, 117 b may be secured to respective recesses119 a, 119 b to form a seal to prevent escape of a pump fluid from thepump fluid paths.

As described in U.S. Pat. No. 8,790,096, fluid may be pumped through thecassette when a series of rollers engage the two or more pump segments103 a, 103 b. The rollers may be radially mounted from an axis ofrotation of the peristaltic pump motor (e.g., a stepper or directcurrent (DC) servo motor, or other motor (such as an alternating current(AC) motor)) and may be configured to compress the pump segments 103 ofthe sheet 107 against the underlying cassette body 105. The first andsecond pump fluid paths (125 a and 135 a, 125 b and 135 b) may fluidlyconnect ports in the cassette body 105, e.g., ports 112 a, 112 b, 112 c,112 d (collectively, ports 112). The ports 112 a-d may providerespective inlets and outlets for fluid being pumped through the pumpfluid paths. As the rollers roll over and away from an inlet port (e.g.,inlet ports 112 a, 112 c), a corresponding fluid bolus may be pulledinto the respective pump fluid path (125 a and 135 a, 125 b and 135 b)through the inlet port (because of a vacuum created by the rollerpushing fluid away from the inlet). As the rollers approach and rollover an exit port (e.g., exit ports 112 b, 112 d), a corresponding fluidbolus may travel through the exit port.

The two (or more) active pump segments 103 in the sheet 107 may be actedupon by a single hub roller assembly. As rollers engage the pumpsegments 103, each roller may first roll over a transition region (e.g.,transition regions 147 a, 147 c) with an underlying transition channel(e.g., transition channels 157 a, 157 c). In some examples, the sheet107 may not include transition regions 147 a-d and the cassette body 105may not include transition channels 157 a-d. As the rollers roll off ofa transition region 147 a, 147 c (and correspondingly, off of atransition channel 157 a, 157 c), the rollers may form an internal sealwithin the pump segment 103 (e.g., at point 161 indicated with dashedlines on pump segment 103 a or at point 169 on pump segment 103 b) bypressing the sheet 107 fully against cassette body 105 at the seal point(in the absence of transition regions and transition channels, theroller may form a seal at the start of the roller's engagement with thesheet 107). The internal seal may move as the roller rolls through the“active” region 163 or 165. As the roller moves, fluid in front of theroller's motion may be pushed through the pump segment 103 resulting influid behind the roller's motion being pulled from the inlet (e.g.,inlet 112 a, 112 c). As the next roller on the roller head approachesthe transition region 147 a, 147 c (over transition channel 157 a, 157c) behind the roller that is currently forming an internal seal, thenext roller may begin to reduce the cross sectional space between thesheet 107 underlying the non-sealed roller and the cassette body 105.Because of the geometry of the transition region 147 a, 147 c and theunderlying transition channel 157 a, 157 c, the non-sealed roller on thetransition region 147 a, 147 c may have fluid under the roller (e.g., inthe transition channel 157 a, 157 c) preventing a seal. As thecross-sectional space is reduced (e.g., as the non-sealed rollerapproaches the seal point or start of the active region 163, 165), fluidbeing pulled by the sealed roller may slowly be constrained. The fluidflow from the inlet as a result of the sealed active roller may slowlybe reduced by the transition roller until the transition roller forms anew seal at the seal point 161 (or 169) and becomes the new activeroller (which may effectively isolate the previous sealed roller). Thesequence may then be repeated as the next roller on the roller headengages the start of the transition region 147 a, 147 c (over transitionchannel 157 a, 157 c).

The sequence of rollers engaging the transition region 147 a, 147 c(over transition channel 157 a, 157 c) and then forming a movinginternal seal (with a subsequent roller slowly reducing fluid flow untilthe subsequent roller forms a seal) may result in cyclical variations(or “pulses”) in the fluid flow/pressure profiles of fluid being pulledfrom the inlet (e.g., inlet 112 a, 112 c) and/or being pushed to theoutlet or exhaust (e.g., outlet or exhaust 112 b, 112 d).

FIG. 2 illustrates a cross-section taken along the line 2-2 in FIG. 1c ,showing the cross-sectional view at that plane with the sheet 107 ofFIGS. 1a-b assembled on the cassette body 105 of FIGS. 1c-d . Theprotrusions 117 a of the sheet 107 can be seen in the recess 119 a ofthe cassette body 105. Line 159 in FIG. 2 marks the center line of thecassette body fluid path transition channel 157 a. As can be seen inFIG. 2, the pump segment 103 a of the sheet 107 has a raised centerportion 171 that is raised over the center of the cassette body fluidpath transition channel 157 a of the cassette body 105. As the pumpsegment 103 a of the sheet 107 continues from the beginning of thecassette body fluid path transition channel 157 a to the beginning ofthe active region 163, the raised center portion 171 gradually increasesin height to a full-height single ridge above active region 163. Theraised center portion 171 continues as a full-height single ridgethrough the active region 163 to the cassette body fluid path transitionchannel 157 b. As the pump segment 103 a of the sheet 107 continues fromthe beginning of the cassette body fluid path transition channel 157 bto the outlet 112 b, the raised center portion gradually decreases inheight. Above outlet 112 b, the elastomeric sheet 107 is similar inprofile to that shown in FIG. 2 above inlet 112 a. The geometry of thepump segment 103 b is the same as that of pump segment 103 a.

FIG. 3 illustrates a cross-sectional view of a part of a first exampleof a peristaltic pump in accordance with the disclosure. FIG. 3 shows aview similar to that of FIG. 2, with a sheet 207 on a cassette body 205.The cassette body 205 may be similar to and have all of the features ofthe cassette body 105. The sheet 207 may be similar to and have all ofthe features of the sheet 107, except that the sheet pump segmenttransition regions of the pump segments of the sheet 207 have adifferent profile than the sheet pump segment transition regions 147 a-dof the pump segments 103 a, 103 b of the sheet 107.

As can be seen in FIG. 3, in the area above the inlet 212 a, the pumpsegment 203 a of the sheet 207 has a sheet pump segment transitionregions 247 a with two raised side ridges 209 that are raised on eitherside of a center portion 208 of the sheet 207, wherein the centerportion 208 of the sheet 207 is the portion of the sheet 207 that isabove the cassette body fluid path transition channel 257 a. The centerportion 208 of the sheet 207 is indented with respect to the two raisedside ridges 209 on either side of the center portion 208. The centerportion 208 comprises an indentation at a position over the center line259 of the cassette body fluid path transition channel 257 a.

As can be seen in FIG. 3, the sheet pump segment transition region 247 acomprises at least one ridge 209, in this example two ridges 209, thathas its maximum height 209H at a position that is offset from the centerline 259 of the cassette body fluid path transition channel 257 a. Inthis example, the height of a point on the sheet 207 represents theheight of the front surface of the sheet 207 as measured from a surfaceof the cassette body 205 that is at the level of the cassette body fluidpath active region, resulting in the height 209H for each ridge 209.

The sheet pump segment transition region 247 a has a thickness at eachridge 209 that is greater than its thickness at the indentation at thecenter portion 208. In the example shown, at each ridge 209, thethickness of the sheet 207 extends for the full range of the height 209Hof the ridge 209. In other examples, the back surface of the sheet 207may be raised above the level of the cassette body fluid path activeregion, such that the thickness of the ridge may be less than the heightof the ridge as measured from the level of the cassette body fluid pathactive region.

The transition region of the flexible sheet 207 may comprise a pluralityof ridges that have their maximum heights at positions that are offsetfrom the center line of the transition channel of the cassette body 205.In the illustrated example, one of the two ridges 209 is on one side ofthe indentation 208, and the other of the two ridges 209 is on anopposite side of the indentation 208. In other examples, other numbersand placements of ridges are possible.

As a pump segment 203 a of the sheet 207 continues from the beginning ofthe cassette body fluid path transition channel 257 a at inlet 212 a tothe beginning of the cassette body fluid path active region(corresponding to active region 163 in FIG. 1c ), the raised side ridges209 gradually decrease in height, until they no longer exist as raisedside ridges at the active region. Similarly, as a pump segment 203 a ofthe sheet 207 approaches the beginning of the cassette body fluid pathactive region (corresponding to active region 163 in FIG. 1c ), theindented center portion 208 gradually increases in height, until itbecomes the full-sized center region over the cassette body fluid pathactive region. The sheet pump segment active region of the pump segment203 a (located above the cassette body fluid path active regioncorresponding to active region 163 in FIG. 1c ) has a similar profile tothe sheet pump segment active region 143 of the pump segment 103 a, witha single raised center portion aligned over the center of the cassettebody fluid path active region. As a pump segment 203 a of the sheet 207continues from the beginning of the cassette body fluid path transitionchannel 257 a at inlet 212 a to the beginning of the cassette body fluidpath active region, the two ridges 209 of the sheet pump segmenttransition region 247 a merge into a single ridge in the sheet pumpsegment active region.

The trailing transition region of the pump segment 203 a from the activeregion to an outlet is similar to the transition region of the pumpsegment 203 a from the inlet to the active region. From the activeregion to the outlet, the raised center portion gradually decreases inheight until it becomes the indented center portion 208 above theoutlet, similar to the indented center portion 208 above the inlet 212 ain FIG. 3. Similarly, from the active region to the outlet, the sideridges form and increase in height, until they become the full height ofthe two raised side ridges 209 as can be seen in FIG. 3.

The sheet 207 has a second pump segment 203 b that is similar to thepump segment 103 b except that it has the same differences from pumpsegment 103 b as pump segment 203 a has from pump segment 103 a. Thegeometry of the pump segment 203 b is the same as that of pump segment203 a.

The profile of the elastomeric sheet 207 in FIG. 3 helps reducepulsations in the peristaltic pump. In the example of FIG. 2, as aroller rolls over an inlet 112 a, 112 c and transition region, theroller presses the raised center portion 171 downward and into thecassette body fluid path transition channel 157 a, 157 c, which cancause or contribute to pulsatory flow. Similarly, in the example of FIG.2, as a roller rolls over a transition region and outlet 112 b, 112 d,the roller again presses the raised center portion 171 downward and intothe cassette body fluid path transition channel 157 b, 157 d, which cancause or contribute to pulsatory flow. By contrast, in the embodiment ofFIG. 3, as a roller rolls over an inlet and transition region, theroller primarily acts against the raised side ridges 209. The raisedside ridges 209 and correspondingly indented center region 208 helpreduce or eliminate downward protrusion of the center region as theroller passes over the inlet and fluid path transition channel, therebyreducing pulsations in the flow. Similarly, in the embodiment of FIG. 3,a roller rolls from the active region over a transition region andoutlet, the roller again primarily acts against the raised side ridges209. The raised side ridges 209 and correspondingly indented centerregion 208 help reduce or eliminate downward protrusion of the centerregion as the roller passes over the fluid path transition channel andoutlet, thereby reducing pulsations in the flow. The raised side ridges209 take pressure off the center region, help prevent the center regionfrom being pushed down into the fluid path transition channel, andaccordingly help reduce pulsations in the flow rate.

As an alternative embodiment (not shown) the cassette body 205 coulditself be provided with one or more raised shoulders or ramps in theareas of the transition regions. These raised shoulders or ramps couldhelp keep the rollers from pressing as much on the center region of theflexible sheet. Similar to the embodiment of FIG. 3, this would takepressure off the center region of the transition region of the flexiblesheet, help prevent the center region of the flexible sheet from beingpushed down into the fluid path transition channel, and accordingly helpreduce pulsations in the flow rate.

FIG. 4 illustrates a top view of a part of a second example of aperistaltic pump in accordance with the disclosure. FIG. 4 shows acassette body 305, in a view similar to that of the cassette body 105 inFIG. 1c . The cassette body 305 may be similar to and have all of thefeatures of the cassette body 105, except with respect to the shape ofthe cassette body fluid path transition channel as shown and asdescribed below. The cassette body 305 may be used with any suitableflexible sheet, such as the sheet 107 or the sheet 207.

The cassette body 305 has a pump interface portion 309 to which anelastomeric sheet (e.g., elastomeric sheet 107 or 207) may be coupled.The pump interface portion 309 has recesses 319 a, 319 b adapted toreceive corresponding protrusions of the elastomeric sheet (e.g.,protrusions 117 a, 117 b). The areas bounded by these recesses 319 a,319 b and the corresponding protrusions of the elastomeric sheetconstitute the areas for fluid flow within the fluid paths defined inpart by cassette body fluid paths 325 a, 325 b. The fluid flows frominlet 312 a to outlet 312 b in a first fluid path and from inlet 312 cto outlet 312 d in a second fluid path.

The cassette body fluid paths 325 a, 325 b include active regions 363,365 that are similar to the active regions 163, 165 in FIG. 1b . Thepump segments include cassette body fluid path transition channels 357a, 357 b, 357 c, 357 d that are designed to reduce pulsations in fluidflow.

FIG. 5 shows an enlargement of cassette body fluid path transitionchannel 357 a. Transition section 357 a includes a bottom surface 381,side walls 382, 383, side wall top edges 384, 385, first end 386 andsecond end 387. The first end 386 represents the end of the cassettebody fluid path transition channel 357 a adjacent the inlet 312 a, andthe second end 387 represents the end of the cassette body fluid pathtransition channel 357 a adjacent the active region 363. The shape ofcassette body fluid path transition channel 357 a is representative ofthe shape of the other cassette body fluid path transition channels 357b-d. In the case of a cassette body fluid path transition channel at theend of a pump segment, such as cassette body fluid path transitionchannels 357 b and 357 d, the first end 386 represents the end of thecassette body fluid path transition channel 357 b, 357 d adjacent theoutlet 312 b, 312 d, respectively.

As can be seen in FIGS. 4 and 5, the side walls 382, 383, and the sidewall top edges 384, 385, gradually get closer together as they move awayfrom the first end 386 and toward the second end 387 of the cassettebody fluid path transition channel 357 a. Thus, the width of thecassette body fluid path transition channel 357 a gradually getsnarrower toward the second end 387 (the width being the dimension acrossthe cassette body fluid path transition channel in a direction along aradius of the pump interface portion). As can be seen in FIGS. 4 and 5,a distance between the two side walls 382, 383 tapers toward the secondend 387. In addition, the side walls 382, 383 are sloped such that theside walls 382, 383 are closer together at the bottom surface 381 thanthey are at the top where they meet side wall top edges 384, 385. As canbe seen in FIGS. 4 and 5, a distance between the two side walls 382, 383tapers toward the bottom 381 of the cassette body fluid path transitionchannel 357 a. The bottom surface 381 also slopes upwardly toward thesecond end 387. The other cassette body fluid path transition channels357 b-d have the same shape as the cassette body fluid path transitionchannel 357 a.

In prior designs such as the cassette body of FIG. 1c , while having abottom surface that is sloped upwardly toward the end of the cassettebody fluid path transition channels 157 a-d (see, e.g., sloped surfaces158 a-d in FIG. 1c ), the cassette body fluid path transition channels157 a-d have a constant width at all places across the cassette bodyfluid path transition channel. By contrast, in the design of FIGS. 4-5,the width of the cassette body fluid path transition channels 357 a-dgradually changes, i.e., getting narrower toward the end 387 on accountof the side walls 382, 383 (and side wall top edges 384, 385) gettingcloser together toward the end 387. In addition, due to the slope of theside walls 382, 383, the width of the cassette body fluid pathtransition channels 357 a-d is narrower at the bottom of the cassettebody fluid path transition channels 357 a-d than at the top.

On account of the geometry as shown in FIGS. 4-5, the fluid flow to andfrom the active region is smoother and more gradual. The tapering of theside walls 382, 383 both toward the end 387 and toward the bottom 381 ofthe cassette body fluid path transition channel 357 a-d creates asmoother and more gradual flow to and from the active region. Thissmoother and more gradual flow reduces pulsations in the flow that maybe present in prior geometries.

FIG. 6 shows a graph comparing a prior peristaltic pump system atconstant speed with a peristaltic pump operated in accordance with thedisclosure at varying speeds. The example prior peristaltic pump systemin the graph of FIG. 6 (labeled “constant speed”) has two pump segmentsand seven rollers, similar to that described in U.S. Pat. No. 8,790,096.The rollers are operated by a stepper motor, having in this example 200steps per revolution of the set of rollers. With each revolution of theset of rollers, each roller passes over each of the two pump segmentstwice. As can be seen in FIG. 6, this example prior system resulted in apulsed flow ranging from a low of about 9.5 ml/minute to a maximum ofabout 13.8 ml/minute. The flow went in cycles, with 14 high points and14 low points, representing the 14 passes of the rollers on the pumpsegments (7 rollers each passing on 2 pump segments). As can be seen inFIG. 6, every other low point appears different, with one set of lowpoints in the range of about 9.5 ml/minute to about 9.8 ml/minute andthe other set of low points in the range of about 10.5 ml/minute toabout 10.8 ml/minute, suggesting a difference between the two pumpsegments.

In accordance with this disclosure, the speed of the motor of theperistaltic pump system was modulated based on a measured flow output.The motor was operated faster in areas of measured low flow and slowerin areas of measured higher flow. FIG. 7 shows a graph of the speedadjustment factor of the peristaltic pump operated at varying speeds inaccordance with the disclosure. Based on the measured flow output, themotor speed was adjusted continuously to speeds between about 0.75 timesthe nominal operating speed and 1.15 times the nominal operating speed.As can be seen in FIG. 7, the compensation was in cycles reflective ofthe pulsing flow, with 14 adjustments above nominal speed and 14adjustments below nominal speed, representing the 14 passes of therollers on the pump segments (7 rollers each passing on 2 pumpsegments).

As can be seen in FIG. 6, when operated at varying speeds in accordancewith the compensation profile of FIG. 6 (labeled “varying speed” in FIG.6), the resulting fluid flow was much smoother, with reduced pulsations.This system resulted in a flow in a narrow range around 12ml/minute+/−0.2 ml/minute.

A method of operating a peristaltic pump in accordance with thedisclosure comprises operating the set of rollers in a rotary manner,such that during each revolution of the set of rollers, each rollermakes one revolution around the pump segments; operating the set ofrollers at a speed higher than a nominal speed during portions of arevolution of the set of rollers that would result in a lower thanaverage fluid flow rate if the set of rollers were operated at thenominal speed; and operating the set of rollers at a speed lower thanthe nominal speed during portions of the revolution of the set ofrollers that would result in a higher than average fluid flow rate ifthe set of rollers were operated at the nominal speed. The portions ofthe revolution during which the set of rollers are operated at a speedhigher than a nominal speed do not need to be all portions of therevolution that would result in a lower than average fluid flow rate ifthe set of rollers were operated at the nominal speed. Similarly, theportions of the revolution during which the set of rollers are operatedat a speed lower than a nominal speed do not need to be all portions ofthe revolution that would result in a higher than average fluid flowrate if the set of rollers were operated at the nominal speed.

The operating of the set of rollers may be performed in a plurality ofcompensation cycles, with each compensation cycle going to a speedhigher than the nominal speed then to a speed lower than nominal speed.The set of rollers may be operated in a plurality of compensation cyclesper revolution of the set of rollers. In some embodiments, the number ofcompensation cycles per revolution of the set of rollers is equal to thenumber of rollers of the peristaltic pump multiplied by the number ofpump segments of the peristaltic pump. For example, in the example ofFIGS. 6 and 7, the peristaltic pump has seven rollers and two pumpsegments, and the compensation cycles per revolution of the set ofrollers is fourteen, as can be seen in FIG. 7.

The operating of the set of rollers may performed in accordance with acompensation profile that determines the speed of the set of rollers,such as the compensation profile shown in FIG. 7. The compensationprofile may be a fixed profile during the operation of the pump, or itmay vary depending on the speed of the set of rollers.

In some embodiments, the compensation profile may be determined duringthe operation of the peristaltic pump. For example, the flow rate may bemeasured and the speed of the rollers adjusted in real time. As anotherexample, the flow rate may be measured and the speed of the rollersadjusted based on one or more recent pump cycles. In other embodiments,the compensation profile may be determined prior to the operation of theperistaltic pump. For example, the compensation profile may bedetermined during testing of the peristaltic pump or during testing of asimilar peristaltic pump.

The compensation profile may be associated with indicia located on aremovable portion of the peristaltic pump. For example, the cassette mayhave a bar code or other machine-readable indicia that informs theconsole of the compensation profile.

Persons of ordinary skill in the art will appreciate that theimplementations encompassed by the disclosure are not limited to theparticular exemplary implementations described above. In that regard,although illustrative implementations have been shown and described, awide range of modification, change, and substitution is contemplated inthe foregoing disclosure. It is understood that such variations may bemade to the foregoing without departing from the scope of thedisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the disclosure.

What is claimed is:
 1. A cassette for a peristaltic pump of anophthalmic surgical system, the cassette comprising: a cassette bodyhaving a front surface and a back surface, wherein the front surface ofthe cassette body comprises a cassette body fluid path, wherein thecassette body fluid path comprises a plurality of ports, a cassette bodyfluid path active region, and a cassette body fluid path transitionregion between one of the ports and the cassette body fluid path activeregion, wherein the cassette body fluid path transition region comprisesa cassette body fluid path transition channel that is recessed withrespect to the cassette body fluid path active region; and a flexiblesheet joined to the cassette body, wherein the flexible sheet comprisesa sheet pump segment with a back surface comprising a sheet fluid pathand a front surface comprising a roller engagement surface, wherein whenthe flexible sheet is joined to the cassette body the sheet fluid pathis connected with the cassette body fluid path to form a pump fluidpath, wherein the sheet pump segment comprises a sheet pump segmentactive region positioned over the cassette body fluid path active regionand a sheet pump segment transition region positioned over the cassettebody fluid path transition region; wherein the sheet pump segmenttransition region comprises at least one ridge that has its maximumheight at a position that is offset from a center line of the cassettebody fluid path transition channel.
 2. A cassette for a peristaltic pumpof an ophthalmic surgical system as in claim 1, wherein the sheet pumpsegment transition region comprises an indentation at a position overthe center line of the cassette body fluid path transition channel.
 3. Acassette for a peristaltic pump of an ophthalmic surgical system as inclaim 2, wherein the sheet pump segment transition region has athickness at the least one ridge that is greater than a thickness at theindentation.
 4. A cassette for a peristaltic pump of an ophthalmicsurgical system as in claim 1, wherein the sheet pump segment transitionregion comprises two ridges, each of which has its maximum height at aposition that is offset from the center line of the cassette body fluidpath transition channel.
 5. A cassette for a peristaltic pump of anophthalmic surgical system as in claim 4, wherein the sheet pump segmenttransition region comprises an indentation at a position over the centerline of the cassette body fluid path transition channel.
 6. A cassettefor a peristaltic pump of an ophthalmic surgical system as in claim 5,wherein one of the two ridges is on one side of the indentation, and theother of the two ridges is on an opposite side of the indentation.
 7. Acassette for a peristaltic pump of an ophthalmic surgical system as inclaim 6, wherein the sheet pump segment transition region has athickness at each ridge that is greater than a thickness at theindentation.
 8. A cassette for a peristaltic pump of an ophthalmicsurgical system as in claim 6, wherein the two ridges of the sheet pumpsegment transition region merge into a single ridge in the sheet pumpsegment active region.
 9. A cassette for a peristaltic pump of anophthalmic surgical system, the cassette comprising: a cassette bodyhaving a front surface and a back surface, wherein the front surface ofthe cassette body comprises a cassette body fluid path, wherein thecassette body fluid path comprises a plurality of ports, a cassette bodyfluid path active region, and a cassette body fluid path transitionregion between one of the ports and the cassette body fluid path activeregion, wherein the cassette body fluid path transition region comprisesa cassette body fluid path transition channel that is recessed withrespect to the cassette body fluid path active region; and a flexiblesheet joined to the cassette body, wherein the flexible sheet comprisesa sheet pump segment with a back surface comprising a sheet fluid pathand a front surface comprising a roller engagement surface, wherein whenthe flexible sheet is joined to the cassette body the sheet fluid pathis connected with the cassette body fluid path to form a pump fluidpath; wherein the cassette body fluid path transition channel comprisesa first end adjacent one of the ports, a second end adjacent the activeregion, and two side walls, and wherein a distance between the two sidewalls tapers toward the second end.
 10. A cassette for a peristalticpump of an ophthalmic surgical system as in claim 9, wherein a distancebetween the two side walls tapers toward a bottom of the cassette bodyfluid path transition channel.
 11. A method of operating a peristalticpump, wherein the pump comprises at least one pump segment and a set ofrollers, the method comprising: operating the set of rollers in a rotarymanner, such that during each revolution of the set of rollers, eachroller makes one revolution around the pump segments; operating the setof rollers at a speed higher than a nominal speed during portions of arevolution of the set of rollers that would result in a lower thanaverage fluid flow rate if the set of rollers were operated at thenominal speed; and operating the set of rollers at a speed lower thanthe nominal speed during portions of the revolution of the set ofrollers that would result in a higher than average fluid flow rate ifthe set of rollers were operated at the nominal speed.
 12. A method ofoperating a peristaltic pump as in claim 11, wherein the operating ofthe set of rollers is performed in a plurality of compensation cycles,with each compensation cycle going to a speed higher than the nominalspeed then to a speed lower than nominal speed.
 13. A method ofoperating a peristaltic pump as in claim 12, wherein the operating ofthe set of rollers is performed in a plurality of compensation cyclesper revolution of the set of rollers.
 14. A method of operating aperistaltic pump as in claim 13, wherein the number of compensationcycles per revolution of the set of rollers is equal to the number ofrollers of the peristaltic pump multiplied by the number of pumpsegments of the peristaltic pump.
 15. A method of operating aperistaltic pump as in claim 11, wherein the operating of the set ofrollers is performed in accordance with a compensation profile thatdetermines the speed of the set of rollers.
 16. A method of operating aperistaltic pump as in claim 15, wherein the compensation profile is afixed profile.
 17. A method of operating a peristaltic pump as in claim15, wherein the compensation profile varies depending on the speed ofthe set of rollers.
 18. A method of operating a peristaltic pump as inclaim 15, wherein the compensation profile is determined during theoperation of the peristaltic pump.
 19. A method of operating aperistaltic pump as in claim 15, wherein the compensation profile isdetermined prior to the operation of the peristaltic pump.
 20. A methodof operating a peristaltic pump as in claim 15, wherein the compensationprofile is associated with indicia located on a removable portion of theperistaltic pump.